1. Field of the Invention
The present invention relates to a semiconductor laser diode and a method of fabricating the same, and more particularly, it relates to a semiconductor laser diode comprising a window structure on a laser beam emission end surface portion and a method of fabricating the same.
2. Description of the Background Art
In order to allow double-layer recording in a recordable DVD system, the intensity of a laser beam applied onto a disc must be increased. In order to improve the intensity of the laser beam applied onto the disk, the light output of a semiconductor laser diode serving as a light source must be increased.
In order to increase the output of the semiconductor laser diode, a COD (catastrophic optical damage: deterioration of a laser beam emission end surface portion) level must inevitably be improved. It is known that COD takes place in the following cycle: When a current is injected into an emission end surface portion having surface states in high concentration, non-radiative recombination takes place through these levels. Thus, the emission end surface portion generates heat. This heat reduces an energy gap of an active layer of the emission end surface portion, to increase light absorption. Thus, heat generation is further increased. The temperature of the emission end surface portion is increased due to this cycle to melt crystals, resulting in breakage of the emission end surface portion.
A semiconductor laser diode comprising a window structure formed by Zn diffusion is known in general as that suppressing such COD, as disclosed in “IEEE Journal of Quantum Electronics”, Vol. 29, No. 6, pp. 1874 to 1877, 1993, for example. In the semiconductor laser diode comprising a window structure formed by Zn diffusion disclosed in this literature, an impurity (Zn) is introduced into an emission end surface portion of the semiconductor laser diode so that Zn introduced into the emission end surface portion of a p-type cladding layer is diffused to extrude toward an n-type cladding layer through an active layer, as clearly understood from Zn concentration profiles before and after the Zn diffusion in the conventional semiconductor laser diode shown in FIGS. 31 and 32 respectively. At this time, atoms constituting well layers and barrier layers of the active layer are mutually diffused to disorder a quantum well structure of the active layer. Thus, the band gap of the emission end surface portion of the active layer widens beyond those of the remaining regions, to reduce light absorption in the emission end surface portion. Thus, the emission end surface portion can be inhibited from temperature rise, thereby preventing from COD.
In a conventional AlGaInP-based red semiconductor laser diode, on the other hand, a band discontinuity value between an active layer and a p-type cladding layer on the side of a conduction band is so small that electrons supplied to the active layer easily thermally overflow from the active layer into the p-type cladding layer. Therefore, a light output value tends to lower with respect to the value of a fed current under a high temperature. Thus, it is disadvantageously difficult to improve temperature characteristics indexing unchangingness of the light output value with respect to the temperature. In order to improve the temperature characteristics by solving this disadvantage, the band discontinuity value between the active layer and the p-type cladding layer on the side of the conduction band must be increased by increasing the carrier (hole) concentration in the p-type cladding layer. In the conventional red semiconductor laser diode, the carrier (hole) concentration in the p-type cladding layer is increased using Zn as an impurity.
In the conventional red semiconductor laser diode with the p-type cladding layer doped with Zn as the impurity, however, the quantity of introducible Zn is so limited that it is difficult to increase the quantity of the impurity (Zn) introduced into the p-type cladding layer. Thus, it is disadvantageously difficult to improve the temperature characteristics of the conventional semiconductor laser diode.